The optical properties of gold nanoclusters of size 2 - 20 have been investigated using time-dependent density functional
theory (TDDFT) to simulate their linear absorption spectra. Relativistic effects have been included by using
pseudopotentials, with the Douglas-Kroll (DK) approximation, and with the zero-order regular approximation (ZORA).
The improved model core potential with scaled relativistic effects (iMCP-SR2) used in combination with either the
BP86, BLYP, or B3LYP exchange-correlation density functional was found to fairly accurately model the spectra of
clusters for which measured spectra are available, although the all-electron ZORA method was best both for accuracy
and computational efficiency. The effects on the optical properties of organic chromophores from coordination with
small gold clusters were preliminarily studied. The extent of enhancement of the absorption properties is seen to depend
on the size and structure of the gold cluster.